The present invention is particularly applicable for connecting branch lines to natural gas pipelines and it will be described with particular reference thereof; however, it is appreciated that the invention has broader applications and may be used in connecting branch lines to various types of pipelines, such as natural gas, oil, gasoline, water slurries, etc.
In construction of a pipeline, many miles of large metal pipe is laid through drastically varying terrain, such as the wilderness of Canada. Such pipelines are extremely expensive and often require a number of intersecting branch lines which are used for compression stations and feeder lines. To reduce the time, simplify the logistics and minimize the initial cost, a pipeline is often laid without all branch connections ultimately required for a given pipeline system. Thus, it is necessary to provide a scheme for subsequently connecting a branch line to the pipeline system. This has been done by a variety of methods. One method is illustrated in U.S. Pat. Nos. 2,771,096 and 2,988,111. A nipple is welded over the pipeline and a temporary valve is connected to the nipple. The remote side of the valve is provided with a boring machine which includes a boring tool that extends through the valve to cut an opening in the side of the pipeline. Thereafter, the valve is closed manually and a sealing member is secured by external means adjacent the pipeline. Thereafter, the valve and boring machine are removed and the pipeline branch nipple is capped. When a branch line is to be connected, the valves and boring machine are again used to remove the sealing member. The valve is ultimately opened manually to connect the branch line onto the pipeline. By this arrangement, a temporary capping unit is provided for the pipeline. However, to connect the branch line, there is a need for a large rotary valve and substantial equipment at the site. The site may be somewhat remote and the special equipment may not be available to persons who are attempting to connect the branch line. Also, this equipment may not be available many years hence. Also, the special equipment is expensive and the valving required for making the branch connection adds drastically to the cost of the branch line connection.
The most common arrangement proposed for providing a temporary cap at a pipeline for subsequent connection of a branch line, involves connecting a rotary valve to a nipple extending from the pipeline at the position of a subsequent connection. The other side of the valve includes a closed nipple. To connect the branch line, the closed nipple is opened and the connection is made. Thereafter, the valve is manually rotated to open the branch line. Such a system involves substantial, initial capital investment. These valves, which may not be used for many years, are expensive and may require periodic maintenance or service. Rotary valves may freeze in the closed position which completely bode against the feasibility of using such an arrangement for a subsequently installed branch line. As can be seen, arrangements for connecting branch lines to an operating pipeline, which branch lines may not be needed for many years, either involves a substantial amount of investment at the time the pipeline is laid or special equipment for making the branch line connection several years hence. Both of these factors are commercially unacceptable to pipeline construction firms.